This invention relates to die casting equipment and methods, and more particularly to die casting molds for production castings having closely spaced projections thereon, such as finned objects for heat transfer, wherein the fins or other projections have limited space therebetween produced by re-entrant portions of the mold, and a method of cooling such re-entrant mold portions to prevent them from sticking to the casting.
Finned objects in the prior art have been produced by several means. Cylinders for air-cooled engines have been sand-cast with external fins, but such fins have been of large cross-section and spacing in relation to their height, and sand-casting is a slow and expensive process.
Finned tubes for heat exchangers are commonly made by sliding thin annuli over the tube and soldering or welding them in place. Finned tubes have also been made by helically winding a strip edgewise around the tube and welding or soldering the inner edge to the tube.
Finned objects have sometimes been made by die casting, but again the fins have been heavy and widely spaced, even with internal passages in the die for water cooling. In some cases the fin-forming portions of the die have been sprayed with water mist while the die is open between shots, or have had an air blast directed into them. A different approach is shown in U.S. Pat. No. 3,595,301 issued July 27, 1971 to Alfred F. Bauer. That patent discloses a method of making die-cast finned objects in which a die is assembled outside a casting machine, then loaded into the machine, the machine closed and a casting shot made, the machine opened and the die containing the cast object removed from the machine, the die disassembled to remove the casting therefrom, and the die parts then placed into a bath to bring them to proper temperature. This is a complex and cumbersome procedure, and if only one die is available the production rate is necessarily slow owing to the number of manual operations which have to be conducted outside the casting machine between shots. If a number of dies are provided to keep the machine busy the cost is correspondingly increased, and extra personnel are needed to carry out the manual operations. Even with the procedure disclosed in the patent, the fins produced by that method are of a height only about three times their thickness at the base.
The present invention overcomes these limitations of the prior art.